Sleep disordered breathing (SBD) occurs when there is a partial or complete cessation of breathing that occurs many times throughout the night. Obstructive sleep apnea (OSA) is a type of SBD that involves cessation or significant decrease in airflow in the presence of breathing effort. It is the most common type of SBD and is characterized by recurrent episodes of upper airway collapse during sleep inducing repetitive pauses in breathing followed by reductions in blood oxygen saturation. The pathophysiology of OSA can involve factors such as craniofacial anatomy, airway collapsibility, and neuromuscular control of the upper airway dilator musculature. Electromyogram studies have shown that the tonic and phasic activity of the main pharyngeal airway dilatory muscle (such as the genioglossus muscle) is progressively reduced from wakefulness to non-rapid eye movement to rapid eye movement.
Continuous positive airway pressure (CPAP) therapy is the frontline treatment for OSA. CPAP therapy utilizes machines, generally including a flow generator, tubing, and a mask designed to deliver a constant flow of air pressure to keep the airways continuously open in patients with OSA. However, the success of CPAP therapy is limited by compliance with reported rates ranging from 50% to 70%. Hypoglossal nerve stimulation (HNS) has now been established as an effective form of therapy for patients with obstructive sleep apnea (OSA) who are unable to tolerate positive airway pressure. This therapy works by protruding and stiffening the tongue muscle thereby dilating the pharyngeal airway. HNS primarily dilates the hypopharyngeal airway, and has a more modest and variable effect on dilation of the retropalatal airway. Patients with significant retropalatal airway collapse (more specifically, circumferential palatal collapse) are not candidates for the only HNS therapy commercially available in the US because of this issue.